/Engine/Source/Runtime/MovieScene/Public/EntitySystem/MovieSceneEntitySystemLinker.h
Register a new extension type for use with any instance of aUMovieSceneEntitySystemLinker
template<typename ExtensionType> static [UE::MovieScene::TEntitySystemLinkerExtensionID](API\Runtime\MovieScene\EntitySystem\TEntitySystemLinkerExtensionID)< ExtensionType > RegisterExtension()